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<H1>SBB -- Integer Subtraction with Borrow</H1>


<PRE>
Opcode       Instruction       Clocks  Description

1C  ib       SBB AL,imm8       2       Subtract with borrow immediate byte
                                       from AL
1D  iw       SBB AX,imm16      2       Subtract with borrow immediate word
                                       from AX
1D  id       SBB EAX,imm32     2       Subtract with borrow immediate
                                       dword from EAX
80  /3 ib    SBB r/m8,imm8     2/7     Subtract with borrow immediate byte
                                       from r/m byte
81  /3 iw    SBB r/m16,imm16   2/7     Subtract with borrow immediate word
                                       from r/m word
81  /3 id    SBB r/m32,imm32   2/7     Subtract with borrow immediate
                                       dword from r/m dword
83  /3 ib    SBB r/m16,imm8    2/7     Subtract with borrow sign-extended
                                       immediate byte from r/m word
83  /3 ib    SBB r/m32,imm8    2/7     Subtract with borrow sign-extended
                                       immediate byte from r/m dword
18  /r       SBB r/m8,r8       2/6     Subtract with borrow byte register
                                       from r/m byte
19  /r       SBB r/m16,r16     2/6     Subtract with borrow word register
                                       from r/m word
19  /r       SBB r/m32,r32     2/6     Subtract with borrow dword register
                                       from r/m dword
1A  /r       SBB r8,r/m8       2/7     Subtract with borrow r/m byte
                                       from byte register
1B  /r       SBB r16,r/m16     2/7     Subtract with borrow r/m word
                                       from word register
1B  /r       SBB r32,r/m32     2/7     Subtract with borrow r/m dword
                                       from dword register
</PRE>

<H2>Operation</H2>

<PRE>
IF SRC is a byte and DEST is a word or dword
THEN DEST := DEST - (SignExtend(SRC) + CF)
ELSE DEST := DEST - (SRC + CF);
</PRE>

<H2>Description</H2>

SBB adds the second operand (DEST) to the carry flag (CF) and
subtracts the result from the first operand (SRC). The result of the
subtraction is assigned to the first operand (DEST), and the flags are
set accordingly.
<P>
When an immediate byte value is subtracted from a word operand, the
immediate value is first sign-extended.

<H2>Flags Affected</H2>

OF, SF, ZF, AF, PF, and CF as described in <A HREF="appc.htm">Appendix C</A>

<H2>Protected Mode Exceptions</H2>

#GP(0) if the result is in a nonwritable segment; #GP(0) for an illegal
memory operand effective address in the CS, DS, ES, FS, or GS
segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code)
for a page fault

<H2>Real Address Mode Exceptions</H2>

Interrupt 13 if any part of the operand would lie outside of the effective
address space from 0 to 0FFFFH

<H2>Virtual 8086 Mode Exceptions</H2>

Same exceptions as in Real Address Mode; #PF(fault-code) for a page
fault


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